Recently, planar displays capable of being made thin are being brought into practical use in place of conventionally used CRTs (Cathode Ray Tubes). For example, organic electroluminescence devices (i.e., organic EL devices) are highlighted as a next-generation display device owing to its self-luminosity and high-speed responsiveness. Further, organic EL devices are also used as a surface emitting element besides being used for display devices.
The organic EL device has a structure in which an organic layer having an organic EL layer (light emitting layer) is embedded between an anode (positive electrode) and a cathode (negative electrode), and is configured to let the light emitting layer emit light by injecting holes from the anode and electrons from the cathode into the light emitting layer to induce recombination between the holes and the electrons.
Further, the organic layer may further contain, if required, a layer for improving luminous efficiency, such as a hole transport layer or an electron transport layer, between the anode and the light emitting layer or between the cathode and the light emitting layer.
As for an example of a method for forming the above light emitting element, the following method has been conventionally employed. First, an organic layer is formed by a deposition method on a substrate on which an anode formed of ITO (Indium Tin Oxide) is patterned. Herein, the deposition method refers to a method for forming a thin film by depositing evaporated or sublimated material on a target substrate. Thereafter, Al (aluminum) layer serving as a cathode is deposited on the organic layer. The light emitting element thus manufactured is occasionally referred to as “top cathode type” light emitting element.
In this manner, for example, the light emitting element in which the organic layer is formed between the anode and the cathode is manufactured (see, e.g., Patent Document 1).
FIG. 1 schematically shows an exemplary configuration of a conventional deposition device.
Referring to FIG. 1, a film forming apparatus 10 includes a processing chamber 11 having therein an inner space 11A. Installed in the inner space 11A are a deposition source 12 and a substrate holding table 15 facing the deposition source 12. The inner space 11A is exhausted via a gas exhaust line 14 connected to a gas exhaust unit (not shown) such as a vacuum pump or the like to be maintained at a specific depressurized level.
The deposition source 12 is connected to a heater 13 such that a source material 12A contained therein can be heated by the heater 13 to be turned into a gas material by being evaporated or sublimated. The gas material is deposited on a target substrate S held on the substrate holding table 15.
By using the film forming apparatus 10, it is possible to form, e.g., an organic layer (light emitting layer) in a light emitting element, an electrode on the organic layer and the like.
However, when a film is formed by using the conventional deposition device, it is necessary to employ a face-down film formation method in which a film-forming surface of a target substrate is arranged to face downward in order to have the source material evaporated or sublimated from the deposition source in the processing chamber be deposited on the target substrate. Accordingly, if the size of the target substrate is increased, handling the substrate becomes difficult. Therefore, there occurs a problem in that the productivity of the film forming apparatus is deteriorated.
Further, in the conventional deposition device, the material evaporated or sublimated from the deposition source may be adhered to other parts than the target substrate, causing particle generation. This may require an increased frequency of removing the adhered material, which reduces the productivity.
In order to prevent material from being attached to portions other than the target substrate, it is preferable to shorten the distance between the deposition source and the substrate (holding table). However, when placing the target substrate near the deposition source that heats the source material to evaporate or sublimate it, the target substrate or the mask on the target substrate gets heated, and the uniformity in the film thickness may become deteriorated. To that end, the deposition source and the target substrate need to be spaced apart from each other with a specific distance.
Further, film formation using, e.g., sputtering method is advantageous in that the direction of the target substrate is relatively free and the productivity is high. However, in this case, larger damages are inflicted on a target object of film formation compared to film formation using deposition method.
When, for example, film formation is performed on an organic layer having a light emitting layer in an organic EL device or the like, damage inflicted on the organic layer by the sputtering may be problematic. In some cases, the organic layer is damaged to deteriorate the quality of the light emitting element by, e.g., particles of a hard metal such as Al colliding with the organic layer at a high speed by the sputtering or ultraviolet irradiated thereon following plasma excitation.
As for the case where a film is formed on an organic layer, the following is an example thereof.
In, for example, a light emitting element using an organic layer and a metal electrode, luminous efficiency may be reduced due to the difference between work functions of the organic layer and the electrode. In order to suppress such decrease in the luminous efficiency, a specific metal-containing layer (e.g., a metal layer or a metal compound layer) may be formed between the organic layer and the electrode (i.e., on the organic layer). In case of forming the layer for suppressing the decrease in luminous efficiency due to the difference between work functions of the organic layer and the electrode (hereinafter, this layer may be referred to as a “work function adjustment layer”), the organic layer may be damaged depending on film forming method (such as sputtering method). Further, some kinds of materials used for forming the work function adjustment layer are not suitable as a sputtering target.
On the other hand, in case of forming the work function adjustment layer by the conventional deposition method, it is difficult to overcome the aforementioned problems such as difficulty in handling a large-sized substrate and deterioration in the productivity.
Besides, Patent Document 2 describes a film forming apparatus for performing film formation by transporting evaporated or sublimated material. However, Patent Document 2 is silent about problems occurred when forming a film on an organic layer having a light emitting layer, and solutions therefor.
(Patent Document 1) Japanese Patent Application Publication No. 2004-225058
(Patent Document 2) U.S. Pat. No. 6,849,241